ci: bump version of pytest

Without this for some reason the following error can happen if when we add
other dependencies in later commits:

> ImportError: cannot import name 'Config' from 'pytest'

(Specifically the dependencies of pycryptodome and pyzipper)

Have to admit I'm not really sure why, and haven't spent that long trying to
work out why, but I think it's reasonable to use a more recent version even
without this issue and not really worth the time investigating it.

pyproject.toml

@@ -20,13 +20,13 @@ classifiers = [
 [project.optional-dependencies]
 dev = [
     "coverage>=6.2",
-    "pytest>=6.2.5",
+    "pytest>=7.0.1",
     "pytest-cov>=3.0.0",
     "stream-unzip>=0.0.86"
 ]
 ci = [
     "coverage==6.2",
-    "pytest==6.2.5",
+    "pytest==7.0.1",
     "pytest-cov==3.0.0",
     "stream-unzip==0.0.86"
 ]